首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   177篇
  免费   10篇
林业   7篇
农学   5篇
  9篇
综合类   37篇
农作物   9篇
水产渔业   10篇
畜牧兽医   104篇
植物保护   6篇
  2023年   2篇
  2019年   2篇
  2018年   3篇
  2017年   6篇
  2016年   3篇
  2015年   5篇
  2014年   5篇
  2013年   10篇
  2012年   4篇
  2011年   7篇
  2010年   7篇
  2009年   5篇
  2006年   3篇
  2005年   7篇
  2004年   7篇
  2002年   4篇
  2000年   2篇
  1999年   4篇
  1998年   5篇
  1996年   2篇
  1992年   2篇
  1990年   9篇
  1989年   6篇
  1988年   4篇
  1987年   4篇
  1986年   5篇
  1985年   4篇
  1984年   2篇
  1983年   4篇
  1980年   1篇
  1979年   1篇
  1977年   1篇
  1975年   2篇
  1974年   2篇
  1973年   1篇
  1971年   5篇
  1970年   2篇
  1969年   5篇
  1968年   3篇
  1967年   3篇
  1966年   7篇
  1965年   1篇
  1963年   1篇
  1959年   1篇
  1955年   1篇
  1954年   1篇
  1953年   1篇
  1947年   1篇
  1936年   1篇
  1935年   2篇
排序方式: 共有187条查询结果,搜索用时 500 毫秒
31.
32.
Cleft palates were induced in newborn pigs of gilts fed Conium maculatum seed or plant during gestation days 30 through 45. Twelve of 23 newborn pigs born to 3 gilts given Utah-grown C maculatum seed and 9 of 12 newborn pigs born to a single gilt given the fresh Utah spring-growth C maculatum plant had cleft palates. The cleft palates ranged from a unilateral cleft, involving only 1 side of the palate, to a full bilateral cleft. Brachygnathia was also observed in some of these newborn pigs with cleft palate. Other malformations were not observed. Chemical analysis of seed and plant samples indicated that gamma-coniceine was the responsible teratogenic alkaloid. A daily dose of plant or seed that provided greater than or equal to 1.07 mg of gamma-coniceine/kg of body weight fed to gilts during the 30th through the 45th day of pregnancy resulted in teratogenic effects.  相似文献   
33.
Diacetoxyscirpenol (DAS) was given IV to pigs (0, 0.5, and 1.0 mg/kg of body weight), cattle (0 and 0.5 mg/kg), and dogs (0 and 0.5 mg/kg). Blood was collected and hemograms were done at 0.5-hour intervals for 8 hours. The animals were euthanatized at 8 hours after treatment, and bone marrow samples were taken and examined by light microscopy. Moderate to severe necrosis of bone marrow hematopoietic elements was found in animals given DAS. The sequential increase in the type and number of abnormal cells in the blood suggested a successive destruction of the hematopoietic elements. A marked left shift in the neutrophil population was found in animals given DAS. Metarubricytes and large platelets were found in the blood of animals given DAS. Lymphocytes were replaced with immature cells. Pathologic changes were most severe in the pigs given a dosage of 1.0 mg of DAS/kg. The order of species sensitivity to DAS was pigs greater than dogs much greater than cattle.  相似文献   
34.
Study was made of the pharmacokinetics and toxicopathy of deoxynivalenol (DON, vomitoxin) given IV to swine. In the 24 hours after swine were given DON, clinical signs of vomiting, diarrhea, muscular weakness, tremors, and twilight coma were similar to those observed with other 12,13-epoxytrichothecenes. Hypoglycemia and pancreatic islet cell lesions were observed which indicated that DON-induced changes in intermediary metabolism may be an insidious aspect of DON intoxication. Histopathologic examination of all organ systems revealed pancreatic acinar and islet cell necrosis and mild lympholysis of the mesenteric lymph nodes. The renal excretion of DON was altered by IV infusion of saline solution. Pharmacokinetic findings may indicate that DON was both secreted and reabsorbed by the renal tubules. The half-life of DON ranged from 2.08 to 3.65 hours. Residues of DON were not found in skeletal muscle of swine at 24 hours after dosing.  相似文献   
35.
The objective of this study was to examine the effects of canthaxanthin (Cx) treatment during in vitro maturation (IVM) of porcine oocytes on embryonic development after parthenogenetic activation (PA) and somatic cell nuclear transfer (SCNT), on intracellular glutathione (GSH) and reactive oxygen species (ROS) levels in mature oocytes, and on gene expression in both PA‐ and SCNT‐derived blastocysts. To determine the optimal effective concentration of Cx, porcine oocytes were cultured in IVM medium supplemented with various concentrations (0, 20, 40 and 80 μM) of Cx for 22 hr. Compared to other groups, supplementation with 40 μM Cx significantly improved blastocyst formation rates after PA (< .05), but no significant differences were observed among groups in total blastocyst cell numbers. Subsequently, oocytes were cultured in IVM medium supplemented with or without 40 μM Cx. Oocytes treated with 40 μM Cx showed significantly increased cleavage and blastocyst formation rates after SCNT compared to the control group (< .05). Moreover, significantly increased intracellular GSH and reduced ROS levels were observed in the Cx‐treated group (< .05). In addition, both PA‐ and SCNT‐derived blastocysts from the 40 μM Cx‐treated group showed significantly increased mRNA expression of Bcl2 and Oct4 and decreased Caspase3 expression level (< .05), when compared with the control group. PA‐derived blastocysts from the 40 μM Cx‐treated group also exhibited significantly decreased expression of Bax (< .05). Our results demonstrated that treatment with 40 μM Cx during IVM improves the developmental competence of PA and SCNT embryos. Improvement of embryo development by Cx is most likely due to increased intracellular GSH synthesis, which reduces ROS levels in oocytes, and it may also positively regulate apoptosis‐ and development‐related genes.  相似文献   
36.
Samenvatting Het genoom van het cassava latent virus (CLV), een geminivirus, bestaat uit twee cirkelvormige, enkelstrengige DNA-moleculen nl. DNA 1 (2,78 kb) en DNA 2 (2,72 kb). DNA, verkregen uitNicotiana benthamiana-planten, die mechanisch waren geïnoculeerd met sap van natuurlijk geïnfecteerde cassaveplanten, bevat naast het enkelstrengige genoom-DNA en de corresponderende open, lineaire en via covalent-bindingen gesloten cirkelvormige, extra-getwiste, dubbelstrengige vormen, een enkelstrengig DNA, dat kleiner is dan het genoom-DNA (c. 1,3 kb). Van dit DNA is aangetoond, dat het fungeert als een defect DNA. Het kleinere DNA interfereert met de functies van het genoom-DNA waardoor de plant minder hevige ziektebeelden gaat vertonen. Het was echter nog niet bekend of dezelfde DNA-vormen in het veld voorkomen in natuurlijk geïnfecteerde cassaveplanten met mozaïeksymptomen. In het hier beschreven onderzoek is aangetoond, dat de DNA-vormen in natuurlijk geïnfecteerde cassaveplanten overeenkomen met die in kunstmatig met het CLV geïnfecteerdeN. benthamiana-planten. De hoeveelheid DNA, kleiner dan het genoom, wordt echter sterk verhoogd door passage van het virus van cassave naarN. benthamiana. De mogelijkheid, dat de hoeveelheid van het DNA, kleiner dan het genoom, in mozaïek-vertonende cassaveplanten gecorreleerd is met de mate van symptoomexpressie wordt besproken.  相似文献   
37.
38.
39.
The trefoil domain (TFD) is a protein structure characterized by six cysteines, which form a typical three-loop structure by three disulphide bridges. It is assumed that two of these loops generate a hydrophobic groove, which could be a binding site for carbohydrate residues or proteins. The zona pellucida (ZP) protein, ZP4, contains such a TFD. The carbohydrate-/protein-binding property of TFD allows us to assume a potential sperm receptor function of this domain. Additionally, gastrointestinal trefoil peptides are stable against proteases; therefore, a structural role of TFD within the ZP might also be possible. We were able to show that the synthesized and natural folded feline TFD (fTFD) expresses the typical protease resistance that vanished under reducing conditions and after substitution of cysteine residues within the peptide. Furthermore, an antibody directed against the first loop of fTFD was almost unable to bind to intact in vitro mature cat oocytes. Pre-incubation of oocytes in the reducing agent (DDT), however, improved antibody binding substantially. Therefore, we suggest structural masking of the fTFD domain within the intact ZP. An interaction between fTFD and feline sperm cells was examined using several methods, including immunocytochemistry, immunoelectron microscopy, co-immunoprecipitation and far western blot, but we found no indication for an involvement of TFD in the primary sperm binding to the ZP. To summarize, there is increasing evidence that the TFD of fZP4 has a structural rather than a sperm-binding function.  相似文献   
40.
Methods to quantify plant available silicon (Si) from Si-based slags for use as fertilizers are not well defined. Although it is possible to estimate total Si from a potential Si fertilizer source; this approach does not represent how much Si is available for uptake by the plant. In this study, Si was extracted from ten sources [Wollastonite W10; calcium silicate slag from the US; calcium silicate from Canada; magnesium silicate; Excellerator; silican gel; 00-00-12 + Si (liquid source) and three types of potassium silicate with different concentrations in the liquid form, K53; K120 and AgSilTM25] using each of the following seven methods: hydrochloric acid (HCl) plus hydrofluoric acid (HF) extraction, leaching column; sodium carbonate (Na2CO3–10 g L?1) + ammonium nitrate (NH4NO3–16 g L?1); citric acid (50 g dm?3 or 5%); hydrochloric acid (0.5 N); neutral ammonium citrate (NAC); and resin (Amberlite IRC-50, pK 6.1). All the Si-containing products were added to pots at rates equal to 600 kg ha?1 of Si based on the total Si extracted. Poa trivialis cv. ‘Darkhorse’ was grown for 24 days with these sources to determine Si plant uptake. Based on the correlation coefficients, the best extractor for available Si in solid fertilizer was determined to be Na2CO3 + NH4NO3, while for liquid fertilizers, the total Si (HCl + HF) was found to be the best. Consequently, regulatory agencies now have two extractors for estimating the plant available Si from fertilizers depending on the physical property of the material (solid or liquid).  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号